What is barnyardgrass?

Barnyardgrass is a fast-growing summer annual grass that’s a familiar problem in gardens, farm fields and wet spots. Simple barnyardgrass identification comes down to one feature most other grasses don’t share: there’s no ligule where the leaf meets the stem.

It sprouts in late spring, grows quickly through summer, produces thousands of seeds and dies with the first hard frost. Next year’s crop comes entirely from that seed, so stopping seed production is the whole strategy.

Barnyardgrass isn’t on Pennsylvania’s noxious weed list. It’s mainly a competitor in vegetable gardens and crops, and an eyesore in new or thin lawns.

Barnyardgrass identification: what to look for

Pull one leaf back from the stem and look at the spot where the blade wraps around it, called the collar. Most grasses have a small papery tab or a fringe of hairs there. Barnyardgrass has nothing at all.

• Leaves: smooth, pale to medium green, fairly wide, with a pale midrib running down the center.
• Collar: no ligule and no ear-like auricles.
• Stems: flattened and often reddish-purple near the base, growing in a loose clump.
• Seed head: coarse and branched, with dense clusters of seeds tinged green to purple. Some plants have bristly awns and some don’t.
• Fall color: plants turn reddish-purple in early fall before frost kills them.

Where it grows in Pennsylvania

Barnyardgrass tolerates wet soil better than most annual grasses, so you’ll find it in low spots, along ditches and in gardens that hold water after a storm. It also shows up in crop fields, roadsides, new seedings and lawns that aren’t mowed often.

It doesn’t handle close, regular mowing for long, so it’s less common in established lawns than crabgrass. In central PA, it’s most often a garden weed, especially in tilled vegetable beds on heavy clay soils that stay damp into June.

Barnyardgrass look-alikes

Large crabgrass is the most likely mix-up. Crabgrass has a membranous ligule, hairy leaves and finger-like seed heads. Fall panicum and the foxtails have a fringe of hairs at the collar instead of nothing, and foxtails have dense, bristly, bottlebrush seed heads.

Goosegrass grows flat in a rosette with a silvery-white center and zipper-shaped seed spikes. If you see a bare collar with no ligule, you’ve almost certainly got barnyardgrass.

Young seedlings are harder to sort out, since most annual grasses look alike at the two- or three-leaf stage. Let a few grow a little bigger, or pull one and check the collar with a magnifying glass. The bare, ligule-free collar shows up even on fairly small plants.

How to get rid of barnyardgrass

Because barnyardgrass is an annual with fibrous roots, pulling is often the best answer in a garden or small lawn patch. The key is to get it before seed heads form in midsummer.

• Hand pulling: grab young plants at the base and pull, or pop them out with a hoe or trowel. It’s easiest after a rain while plants are still small.
• Hoeing and cultivation: in vegetable beds, shallow hoeing of seedlings every week or two in early summer keeps them from getting a foothold.
• Bag seed heads: if plants have already headed out, bag them rather than tossing them on the compost pile.

Cultural control. In lawns, thick turf is the best defense. Fertilize properly, water during drought, use grass species suited to your site, and overseed thin areas in early fall. Mowing regularly also keeps it from setting seed. In gardens and beds, a layer of mulch or straw from a clean source smothers seedlings. If water stands in a low spot every time it rains, fixing the drainage removes the conditions it likes.

Chemical control. Preemergence products applied in spring, before soil temperatures climb into the low 60s, prevent most seedlings. Active ingredients Penn State lists for lawns include prodiamine, pendimethalin and dithiopyr. For plants already up in a lawn, selective postemergence options include fenoxaprop, quinclorac, topramezone and mesotrione, which work best on young plants. Read and follow the product label, which is the law, and confirm the product is labeled for your turf type or for garden use before you buy. Applying herbicides for hire in Pennsylvania requires a PA Department of Agriculture pesticide applicator certification, so larger lawn programs belong with a licensed lawn-care company.

Keeping it from coming back

Every plant that goes to seed adds thousands of seeds to next year’s supply, so the first year of pulling is the hardest. Stay on top of it before July and the patch shrinks noticeably the following season.

Bring in topsoil, compost and straw only from sources you trust, clean the mower after cutting a weedy area, and keep garden soil covered between crops. A dense lawn and good drainage in low spots will do most of the long-term work for you.

Questions we get about barnyardgrass

Similar weeds

Large CrabgrassDigitaria sanguinalisFall PanicumPanicum dichotomiflorumGiant FoxtailSetaria faberi